The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Sunday, February 24, 2008

Cliff Swallows Are Returning to South Texas by Ro Wauer

One sure sign of spring is the arrival of cliff swallows. These little birds build their mud-pellet nests under highway bridges and similar structures throughout South Texas. Colonies of from 35 to 200 individuals can usually be found at all the area’s concrete bridges and overpasses. They arrive in South Texas by early March and leave their nesting sites by the end of August. A few migrants can usually be found through October. Our cliff swallows spend their winter months in South America.

Nest-building is an amazing activity. Although some cliff swallows may only refurbish an old nest, most began anew by constructing a retort- or gourd-shaped structure (tubular entrance to a spherical cavity) from thousands of tiny mid pellets that they paste together literally one a time. They congregate at mud puddles or along the banks of streams to gather mud that they shape into round pellets in their beaks. They then methodically construct their nests. Construction time lasts for four to fourteen days, depending upon the availability of mud, distance to the source, and an adequate food supply. They then line their nests with grass and feathers, and the females lay four or five spotted eggs. Fledging occurs in 21 to 24 days.

Biologists have discovered that cliff swallows practice “intraspecific brood parasitism,” by laying eggs in nests other than their own. And, surprisingly, some individuals can transport their eggs to another nest. They may even toss out an egg, presumably to replace it with their own. As many as twenty-five percent if all cliff swallow nests in a colony may be parasitized.

Cliff swallows are one of the square-tailed swallows, in comparison with the long-tailed barn swallow and fork-tailed tree, bank, and rough-winged swallows. Cliff swallows possess a buff-colored rump and cheeks, pale forehead, and blackish throat and back. They are most closely related to cave swallows, which we also have in South Texas. While cliff swallows nest in open places, cave swallows building their nests in twilight sites, such as in the entrance to caves, in culverts, and other closed structures. Cave swallow nests are cup-shaped instead of gourd-shaped

All swallows are insect-eaters, taking millions of flying insects daily. One report stated that 35 cliff swallows collected in the vicinity of cotton fields in Texas had consumed 687 boll weevils, averaging 19 in each bird’s stomach. Beetles of all types are readily consumed. Other food types include ants, bees and wasps, flies, and a number of true bugs. Various small fruits are also eaten after the nesting season.

Cliff swallows are wonderful neighbors for a number of reasons. Not only do they eliminate many of our insect pests, but they provide one more reason to admire and wonder about our natural environment.